The pciPassthru.64bitMMIOSizeGB value changes automatically upon GPU VM power on in ESXi 9.1

Products

• VMware vSphere ESXi

Issue/Introduction

In VMware vSphere ESXi 9.1, when manually configuring the pciPassthru.64bitMMIOSizeGB advanced option for a GPU-enabled Virtual Machine (VM), the entered value is automatically changed or overridden to a different value upon powering on the VM.

Environment

VMware vSphere ESXi 9.1

Cause

ESXi 9.1 introduces a new mechanism that derives VM MMIO sizes automatically, which overrides manually entered pciPassthru.64bitMMIOSizeGB values.

Resolution

To retain manually entered MMIO size values, the automatic MMIO sizing mechanism must be disabled on the affected Virtual Machine.

1. Power off the affected Virtual Machine.

2. Edit the Virtual Machine settings and navigate to Advanced Options (Configuration Parameters).

3. Add the following parameter to disable the automatic calculation: pciPassthru.mmioSizeAutomatic = "FALSE"

4. Power on the Virtual Machine.